1. Field of the Invention
The present invention relates generally to tension control apparatus and more particularly to an improved control apparatus which is able to maintain constant the letoff tension characteristic of a letoff beam of material throughout the starting, normal running, and stopping operational modes of the letoff beams during unwinding of the same.
2. Description of the Prior Art
In the preparation of warp for a loom, it is desirable to control the tension of the warp threads at a very low tension level or value and in addition, to maintain such tension level substantially constant, even during the starting and stopping operational modes of the slasher. Newer processing techniques however, have facilitated a considerable increase in slashing speeds such that the letoff braking systems conventionally employed within the apparatus can no longer maintain the letoff tension at the required values or levels.
In addition, it is well-known that the inertia characteristics of the letoff beams are such as to require that the braking of the letoff beams be in fact controlled in such a manner that the braking is reduced or rendered completely ineffective during acceleration periods, maintained constant during normal running periods during which the material is being transported at a substantially constant rate of speed, and increased during deceleration periods.
Furthermore, as the letoff beams are emptied, the effective braking levels must be reduced due to the fact that the radial distance of the wound beam material, from which the particular material is being unwound at a predetermined time, is constantly being reduced. Still further, the inertia characteristics of the letoff beams are constantly changing as the beams are emptied and this phenomenon continuously alters the braking requirements. It has been observed that conventional control apparatus simply cannot adequately control the tension levels required under such continuously changing and diverse conditions.